Discover the importance of tangency in creating alignments within Sybil 3D. Learn how to maintain tangency and avoid common errors in your design process to make for a smoother driving experience.
Key Insights
- Tangency is vital in Sybil 3D when creating alignments; it ensures tangent objects inside of an alignment, making the alignment design more effective and the driving experience smoother.
- Sybil 3D has a feature that maintains tangency when using grip edits. However, care should be exercised when creating an alignment from a polyline, as it can lead to a lack of tangency if not handled correctly.
- While creating alignments from polylines can potentially lead to tangency errors, it is possible to achieve tangency in this way. The fillet command is a useful tool for creating curves that are tangent to the two selected objects.
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In this video, we're not going to go ahead and draw anything inside Sybil 3D, we're just going to talk about some ideas inside Sybil 3D as we alluded to in the previous video. And that idea that we're going to be talking about is tangency.
When we created our first alignment based on a polyline, we had an error come up. And if I hover over it, you can see right here, it says tangency violated. Tangency is a very important factor inside Sybil 3D when we're talking about alignments.
Sybil 3D likes to make sure that there are tangent items or tangent objects inside of an alignment. So tangency being that we have a line, and then that curve comes off of that line and is tangent to that line, and then tangent to the next line, or tangent to another curve. So the reason for tangency being important is because it makes it, it's kind of an essential design point inside of creating alignments.
Having breaks in an alignment that isn't tangent doesn't make for a nice driving experience. And so oftentimes you want to make sure your alignments are tangent. So from here, what we can see is that if we go to our alignment that we created using our alignment creation toolbar, and I zoom in, you'll notice that we know that we have tangency because we have this image of this line coming out from that line here, and then intersecting this line here.
These lines are showing us our tangency. And so from here, we can see that we have tangency because when I go ahead and try and use these grip edits, Sybil 3D is going to maintain my tangency because of how important tangency is inside of Sybil 3D. So I can click on the script for move or break apart.
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So I can break apart my tangency and not have them linked to each other, but I want to go ahead and just move my PI. So I'm going to go ahead and click on it. And what you'll see is Sybil 3D is going to maintain my tangency.
Now, if I went and I clicked on this, this is changing the radius of my curve. So I'm going to go ahead and slide it in and out to change how I'm doing the radius of my curve. Then I have the options for same thing here, stretching my curve to a specific point.
So I could lock it into that point here. Then I have the grip edits for the end of the curve, so I can slide it back and forth along this line or back and forth along this line. Now, if I go up to the alignment that we created that has the error and tangency, what you'll notice is that I don't have as many grip edits.
If I go here and I select one of these grip edits, you'll notice I can take this line and move it severely out of tangency, or I can take this grip edit here for this curve and make it again, severely out of tangency. Now, this is the reason why I don't often recommend people create alignments using the from objects inside civil 3D, simply because if you're creating an alignment from a polyline and you're not careful, you can have a alignment that doesn't have tangency and it's very hard to fix. Now you don't run into this when you use the alignment creation toolbar.
Now that's not to say that you can't create alignments with polylines that have tangency. You just have to be very careful and you have to go about it like we were building our alignments when we use the alignment creation toolbar. So for example, if I was to type PL for, for polyline and I drew in a polyline and then I use the fillet command and I typed in a radius of 50 feet and I filleted between this line and this line with a radius of 50 feet, that's almost identical to creating our alignment tangent to tangent and then adding in our free curves between entities.
I used a fillet command which the nature of a fillet is that it wants to create a curve that is tangent to the two objects that I'm selecting using a radius that I've told it to use. So because of that, if I took this polyline and I went up to alignments and chose create alignment from object, selected this polyline and hit ENTER and then I hit ENTER to select the direction of my alignment. I'm going to go ahead and have the name of test.
I'm going to have a center line. I'm going to use the proposed alignment style. I'm going to go ahead and uncheck add curves between tangents and I'm going to go ahead and click okay.
So from here what you'll notice is that if I select this it doesn't quite look like my drawing here because I don't have these tangency lines, but that's just a matter of my grips. If I went and I grip edited this, what you're going to see is that as I move things around, so as I as I change this curve length, the same thing here, if I change this curve length here, my tangencies will start to show up. These are these endpoints that this is what a alignment without a combined PI looks like.
If I was to break apart that PI like I had shown here in the grip edit, this is a broken apart PI, but because we use that fillet command with that polyline, we have tangency. Civil 3D created this alignment and it maintains the tangency now. So it's not impossible to create an alignment from an object and have tangency.
It's just more difficult and that's the main reason why I don't recommend creating alignments from polylines. So what I'm going to go ahead and do is I'm going to grab this. I'm going to delete it out of my drawing.
I'm going to zoom back out. I'm going to save and then I'll meet you in the next video.
